A heretofore known prior art cycling-type continual quick service valve device has two valves operatively connected, one directly and the other by a lost-motion connection, to an abutment that has a pair of chambers disposed on the respective opposite sides thereof that are charged respectively with fluid under pressure from a train brake pipe via two restrictions of unequal size the smaller restriction constituting two chokes arranged in series. A reduction of train brake pipe pressure effected by an engineer's brake valve device causes backflow of fluid under pressure through these two restrictions of unequal size to thereby establish successive differential fluid pressure forces that act in opposite directions on the abutment to cause it to sequentially operate the one valve to release fluid under pressure from the train brake pipe and the chamber at one side of the abutment and thereafter the other valve to release fluid under pressure from the chamber at the opposite side of this abutment and a quick service chamber connected thereto to atmosphere until the two valves terminate the release of fluid under pressure from both the train brake pipe and the quick service chamber to atmosphere. This prior art cycling-type continual quick service valve device will continue to operate to sequentially vent the train brake pipe and the quick service chamber in cycles so long as the engineer's brake valve device is effective to release fluid under pressure from the train brake pipe to atmosphere.
It is apparent that the size of the smaller of the two restrictions determines the times required to establish the first differential fluid pressure force on the abutment when an initial reduction of pressure in a train brake pipe is effected by means such as an engineer's brake valve device.
Furthermore, it is apparent that the size of this smaller restriction determines the time required to establish equal pressures in the chambers on the respective opposite sides of the abutment upon termination of the release of fluid under pressure from these chambers by operation of the two valves of this continual quick service valve device while the engineer's brake valve device remains effective to continue the release of fluid under pressure from these chambers to atmosphere. Thus, this smaller one of the two restrictions determines the time required for this prior art cycling-type continual quick service valve device to complete one cycle. Consequently, it will be obvious that the time required for completing one cycle can be reduced by reducing the time required to establish equal pressures on the opposite sides of the abutment subsequent to operation of the continual quick service valve device to terminate the release of fluid under pressure from the train brake pipe and the quick service chamber to atmosphere.
The Association of American Railroads specifies that leakage from a train brake pipe must not reduce the pressure therein more than five pounds per square inch in one minute. Therefore, the difference in size of the above-mentioned two restrictions in the prior art continual quick service valve device must be such that a reduction in brake pipe pressure of five pounds per square inch in one minute as the result of leakage of fluid under pressure from the train brake pipe will not establish, as the result of flow of fluid under pressure from the chambers at the respective opposite sides of the abutment to the train brake pipe, the differential fluid pressure force on this abutment required to operate the two valves connected thereto in the manner described above. Accordingly, it is apparent that the allowable brake pipe leakage dictates that the size of the smaller of the two restrictions cannot be so small that the maximum allowable brake pipe leakage would cause an undesired operation of this prior art cycling-type continual quick service valve device.
Accordingly, it is the general purpose of this invention to provide a cycling-type continual quick service valve device, that has an abutment directly connected to a stem that operates one of a pair of valves and a lost-motion connection with the other valve, with novel communication means through which fluid under pressure may be supplied to and released from a pair of chambers at the respective opposite sides of the abutment. This novel communicating means is so constructed that these chambers may be initially charged at unequal rates from a train brake pipe, the communication with that one of the two chambers that is charged at the slower rate being so constructed as to provide that fluid under pressure may be supplied to this chamber at a faster rate than fluid under pressure may be released therefrom thus enabling fast equalization of pressure between the two chambers upon the pressure in the other chamber exceeding that in the one chamber subsequent to operation of the two valves to terminate the release of fluid under pressure from these chambers to atmosphere, yet insuring that these chambers are charged at unequal rates from a train brake pipe, and that, upon an initial simultaneous release of fluid under pressure from both chambers in response to a reduction of pressure in the train brake pipe effected by the release of fluid under pressure therefrom, the rate of release of fluid under pressure from the other chamber exceeds the rate of release from the one chamber. This construction provides for both fast cycling of this continual quick service valve device and also that it is not operative in response to train brake pipe leakage up to the maximum amount allowable.